But since I live in Tibet, I am glad you brought this one up.
Please tell me what was the point mutation that a Tibetan got within the past 5000 years, that was then selected for over a series of generations, with those without the mutation being rejected by natural selection, until it spread to all the inhabitants of Tibet (and Qinghai). Walk me through this one if you would.
And since the topic is about skeletal systems, and the like, please walk me through how this "random point mutation" that you are going to tell me about relates to building a new skeleton, limb, or complex new trait.
adaptation upon adaptation upon adaptation = macroevolution
Bolder-dash writes:
I believe in adaptation, you got me there.
How much adaptation do you believe in?
Can you get a Polar Bear and a Grizzly Bear from a common ancestral group? (The differences are adaptions).
If so, can you get all bears from a common ancestral group?
If not, why not? It's just adaptation.
On skeletons: There are examples of mutations in modern human bones that could conceivably be advantageous in certain circumstances.
Some of the rarer forms of Polydactyly is one. It's common for people to be born with extra digits on their hands and toes (about 1/500 of the population), but most are useless.
However, some do produce functional new digits that are actually separate from the others. Because we have well shaped hands, and already have the optimum number of digits, these extras would not be advantageous in our present circumstances.
However, if that weren't the case, these rare forms of polydactyly illustrate how mutation can be creative in the kind of dramatic way you seem to be looking for.
Another is single mutations that can both decrease and increase bone density all over the body. Again, we probably have about the right optimum, because we don't break our bones often enough for the increased density (stronger, heavier bones) to be particularly advantageous. But some people do have them, and you can see the potential flexibility which would be available for selection were we living close to nature and under pressure.
Perhaps more common than dramatic changes like increasing a digit are exaptations of existing bones for new purposes, like the Panda's "thumb", a sesamoid bone put to new use.
But how could all the necessary orders be given to create that great potential of variation?
There are two things here:
First, do you really think DNA needs to be given orders to mutate?
And, second, you missed a subtle grammatical point there: I didn’t say that there is great potential for variation (although there is), I said that variation has a great potential to affect fitness.
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ICANT writes:
What mechanism would cause the mutations to mutate (mess up the DNA enough times) to get the proper changes to create the foot?
There are always mutations happening. They are a normal part of the background chemistry of life. They happen because chemical reactions are messy and subject a large number of environmental gradients that will impact the products that the reaction produces.
And, there is also always selection happening. Selection fluctuates over time: it favors one thing, then another, then another. And, each change unlocks new physiological, ecological and behavioral possibilities that can also impact how selection is manifested. The end result is that what constitutes a proper change is entirely subjective: what is proper is determined by which of the current options are most successful.
Ancient organisms developed movement capacity by the gradual accumulation of traits the made movement more efficient than it previously was. Ancient organisms thus developed tissues that could contract and contort the body. Ancient organisms that accidentally secreted minerals into various locations in the body also had a degree of protection from predators, and a useful anchor point to help the contracting tissues perform their functions.
The result was organisms with lots of knobs of mineralized bones and lots of lobes of contractile muscles, and all that was required was for natural selection to amplify those organisms whose bones were arranged in such a way that muscle action was more efficient.
Concurrently, organisms also began using limbs in different ways, thus modifying how selection acted on them. Limbs could be used first only for thrashing about in the water to induce movement or for angling to help steer movement into useful directions. Natural selection amplified the most efficient forms of thrashing until it became the graceful, coordinated motion we see today.
Another success came when thrashing a limb about struck the limb against a solid surface, which gives the organism an added boost due to Newtonian action/reaction. Then, behaviors for increasing the amount of pushing off of solid objects were amplified, and selection favored more coordinated and more efficient forms of pushing off, which caused specific configurations of bones, joints and muscles in the limbs to be amplified in the population. The ability to do the same thing out of the water, where the body’s weight had be born by the limb, was another step forward.
It really isn’t that difficult to envision this process. Just remember that, at every step, there is variation in anatomy and behavior; and that this variation is different from the variation that existed at the last step, because messy chemistry is continually causing changes; and that the most successful, most efficient and most reliable features and behaviors tend to be amplified in the next generations due to the advantages they bestow on their owners.
I think this is a horrible example, for three reasons:
1. In all the history of all the tetrapods in all the world there has never been a line of tetrapods that reversed the orginal reduction to pentadactyl "hands". Many lineages have reduced that number, none have increased it.
2. Most (not all) six fingered individuals are the result of a development defect not a genetic mutation.
3. It suggests that the primary mode of evolution is through that kind of jump when, in face, there is every reason to think that the primary mode of evolution is vastly more gradual.
Is it really that hard to imagine the first opposable thumb showing up out of the blue?
It may or may not be hard to imagine, but it's not what happened. In fact, primates evolved from tree climbing ancestors who ran along branches, in these ancestors the thumb-to-be spread from the other digits giving a wider running surface, suitable for gripping the top of branches in a small mammal. It was only later that the thumb continued its separation and formed the kind of oppositional arrangement familiar to us.
Thumbs, like nearly any other feature you care to mention, came about by very, very gradual changes not saltational jumps.
Mutations which could possibly, with even the greatest stretch of imagination, actually BENEFIT an individual in the right circumstances.
Tetrapods occasionally produced small, unpaired bones between the paired nasals which articulated with the premaxilla. The appearance of internasals is an example of random genetic drift of a minor mutation which results in a benefit (an additional tooth bearing bone).
The development of the rib serves as another example. The earliest tetrapod ribs were independent of the vertebral column. A mutation of the Hox gene (an increase in the number of copies of the gene) led to fusion of these ribs to the spine. This fusion disengaged the rib cage from the musculature of the body and allowed for greater ventilation (the animal can breathe more easily).
Mutations which could possibly, with even the greatest stretch of imagination, actually BENEFIT an individual in the right circumstances.
Compare the human and chimp genomes. Amongst those differences are the beneficial mutations for chimps in their environment and the beneficial mutations in our environment. Those differences are responsible for the morphological and physiological differences between chimps and humans. It is a rather simple concept.
Thumbs, like nearly any other feature you care to mention, came about by very, very gradual changes not saltational jumps.
Sure, hence my point about the Panda's "thumb", above.
However, the creationists on the thread are asking for dramatic novelty from mutations, and the rare functional extra digits show that it's possible. The thread starts off with someone listing the number of bones in our body, as if the implication is that mutations can never create extras, so I point out that it can, and still does.
Much better for Bolder Dash is my question about bears. If he believes in adaptation, where does he put the limit on adaptation? How many adaptations is a population group allowed to make over time?
However, the creationists on the thread are asking for dramatic novelty from mutations, and the rare functional extra digits show that it's possible. The thread starts off with someone listing the number of bones in our body, as if the implication is that mutations can never create extras, so I point out that it can, and still does.
True, but I would argue that Creationists are asking for something that is neither necessary nor particularly illustrative of evolution. By pointing to the tiny number of dramatic mutational changes out there, we simply reinforce the notion that these dramatic changes are a necessary part of Evolutionary theory whereas, of course, they're not.
Better, I think, to keep banging on the central drum of gradual change.
Thumbs, like nearly any other feature you care to mention, came about by very, very gradual changes not saltational jumps.
I have no doubt that you are correct. I was just trying to show a clear, present day example of the existence of the mechanism that allows for the change or evolution from one form to the next.
I have asked repeatedly for you to produce the evidence, any evidence, that a random mutation caused the beginning of a new functioning limb or system.
You can't do that. Mobiogirl it seems just tried, and I don't think anyone could call that a success.
She demonstrated that you were talking nonsense when you said, "We don't see sporadic examples of people born with excess cartilages in random areas, or lubricant forming between some peoples finger joints, or extra ligaments appearing in some individuals which causes some difference of their physical capabilities."
Here is an example of a woman with two patellas: 403 Forbidden
There is cartilage and ligaments attached to both patellas and there are joints between the two patellas and between the extra patella and the femur. She had an extra bone with associated cartilage, ligaments and joints so your statement that we don't see these things is wrong.
Here is an example of a known change to a known gene that suppresses limb development on the abdominal segments of insects: How insects lose their limbs | Nature Here is a quote:
The work of Galant and Carroll1, and Ronshaugen et al.2, is a striking demonstration of the importance of protein evolution in the diversification of arthropod limbs. The analysis2 of the crustacean Ubx protein provides a particularly rigorous standard for future evo—devo studies, in that these authors identified the exact amino-acid substitutions that are responsible for the suppression of insect limbs.
So we see that mutations can make radical changes to limb development.
As a direct response to your question
I have asked repeatedly for you to produce the evidence, any evidence, that a random mutation caused the beginning of a new functioning limb or system.
So, here we have a person with 12 functioning fingers and toes. Now, yes, it is not a direct advantage to survival in this case, but at least it helps you see that it is not impossible for 4 entire functioning digits to spring up in humans.
Then there are the Vadoma tribe where a dominant mutation in chromosome 7 is quite common. It results in a completely different foot morphology. The Vadoma people claim that it doesn't impede running at all.
Lets start out here by asking the simplest of questions. How did Evolution create the more than 1200 bones, joints and muscles and manage to put them all in just the right position performing the exact needed functions?
That's an easy one: it did it gradually, starting from simple beginnings and progressing from there. The Human skeleton is an example of the current mammalian state of the art.
It gives examples of simpler knees than those found in mammals and we see examples of possible intermediate stages from the simplest knees to the more complex.
Note: I am not saying that any of the example animals used were our ancestors; I am saying that these are living animals with fully functional knees that nevertheless range from the simple to the more complex. So we know from them that simpler knees can function, that knees do not have to be complex to function and that our ancestors' knees could have been similar to those we see in living animals today.
How did Evolution create the more than 1200 bones, joints and muscles and manage to put them all in just the right position performing the exact needed functions?
The incidence of joint and skeletal injury show that our joints and skeltons do NOT perform the exact needed functions. I'm not talking about dramatic assaults, say those caused by car crashes. I'm talking about sports injuries, cruciate tendon injuries from soccer, or back injuries from lifting moderate weights. We have moderately functional joints, they are certainly not up to the strains that our leisure or work activities require yet they are good enough for our species to reproduce itself. That is all that evolution requires.
Our current skeletons are the result of large numbers of trial and error experiments. Every embryo conceived is a genetic crap shoot. Every one has random genetic changes, differences from its parents. These differences could be disastrous to the embryo, neutral, or beneficial. The one thing that every embryo had in its favor was that it was a, usually minor, recombination of the genes from fully functioning parents (parents that were functional enough to breed and rear children). Every one was the offspring of a long line of winners.
Every animal born is an experiment, we are all different from our parents. Some people are born with disabilities, some people are gifted athletes. The details of my skeleton and joints are different from the details of those of either of my parents. And I'm not just talking about changes due to sexual dimorphism; my sisters differ from my mother. Yet we all have functional skeletons. There is not one perfect skeleton that we must not deviate from. If there was only a small set of viable solutions for skeletal conformations then either all people would be uniform or we would see large numbers of disabled people. We see neither so we know that skeletons don't have to be conform to an exact specification in order to function. We can also guess this because our skeletons change as we grow. Young children have large parts of their skeleton comprised of cartilage instead of bone, even well after their first decade. Our limb proportions, the curvature of our spines, the fusion of various bones change from child to adult to old adults.
So we know that there is room for variety in skeletons, room for experiments. We know that animals have reasonably different skeletal arrangements from what humans have so we know that there is not one true form that must be hit first time.
We also know that human skeletons vary even inside a single generation. We know that skeletons change between generations (my parents were thick set, I am not), we know that these changes are viable (I am reasonably athletic though I do suffer from occasional, mild backache). So why can't change happen over time? Viable offspring subtly different from their viable parents.
There are 5 basic types of joints: ball-in-socket, hinge, gliding, pivoting, and fixed. Each type is specifically appropriate for its particular motions. How did Evolution manage to put the correct joint in the appropriate position?
These specializations can develop over time from simpler joints and these types of joints merely refer to different types of movement of the joints. This movement is influenced by shape and the conformation of ligaments that connect the joints, tendons that cross them and the orientation of fibers in their joint capsules. The paper that I linked to above shows various plausible intermediate configurations of joint capsules, tendons, ligaments and the acquisition of the patella.
The collateral ligaments of the knee are localized thickenings of the joint capsule so its easy to see how they may have evolved. The patella is just a bone that developed inside a tendon. The synovial fluid in joints is just an excretory product of some cells that line the joint cavity. There is nothing here that seems impossible to evolve.
Edited by scarab, : The original could have been taken to mean that we evolved from knees. That wasn't what I meant :-)
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